In the semiconductor industry, an integrated circuit chip with high performance needs lowest possible RC time delay and signal crosstalk; therefore, a low dielectric constant material is required to be filled between the low resistance copper wires and the wiring layers to decrease parasitic capacitance, so as to improve the performance of the device. In the last ten years, researches on ultra-low dielectric constant materials are increasing in the semiconductor industry. In the process of integrated circuit, the ultra-low constant materials have to satisfy multiple key performance indicators, such as: adequate mechanical strength to support multi-layer interconnect structure, high Young's modulus, high breakdown voltage, low current leakage, high thermal stability, high adhesive strength, low moisture uptake, low film stress, high planarization capacity, low thermal expansion coefficient and compatibility with chemical mechanical polishing process, etc.
Carbon doping and micro-pore forming are effective methods to decrease the dielectric constant (k value). In the present sub-45 nm technology, the carbon-doped porous silicon oxide film with Si—C bonds is generally used as the ultra-low dielectric constant insulating material. Wherein the dielectric constant of the carbon-doped silicon oxide has a linear relationship with the density thereof, the lower the density, the lower the K value; the dielectric constant of the microporous material is also related to the porosity thereof, wherein the higher the porosity, the lower the k value.
However, with the requirement for decreasing the dielectric constant of the dielectric material, the porosity and carbon content of the dielectric material are increasing and the structure of the dielectric material are becoming more and more loose. In the subsequent dry-etching process, plasma of the etching process would break the Si—C bonds at the sidewalls; and then the hydroxyl group (OH) contained in the chemical agents used in the subsequent wet cleaning process, will replace C in the Si—C bonds, to form Si—OH, which will decrease the porosity and pores' diameter of the ultra-low dielectric constant (ULK) film, thereby causing the value of dielectric constant k to increase. In addition, since the —OH is easy to absorb the moisture or other impurities in the air, the Si in the ultra-low dielectric material is easy to be consumed under the temperature of the subsequent processes, which will causes an increase in the value of dielectric constant k and the critical dimension (CD).